Process for producing metals and alloys



Patented June 23, 1925.

UNITED STATES 1,543,321 PATENT OFFICE.

SVEN DAGOBERT DANIELI AND 130 MICHAEL STURE KAI-LING, OI TROLLHATTAN,SWEDEN, ASSIGNORS TO AKTIEBOLAGET FERROLEGERINGAR, OF STOCKHOLM, SWEDEN,A JOINT STOCK COMPANY LIMITED 01 SWEDEN.

IROCESS FOR PRODUCING METALS AND ALLOYS.

No Drawing.

To all whom it may concern:

Be it known that we, SvnN DAGOBERT DAN- IELI and Bo MICHAEL STUREKALLING, sub jects of the King of Sweden,'and residing in Trollhattan,in the Kingdom of Sweden, have invented Certain new and useful Im-'provements in Processes for Producing Metals and Alloys; and we dohereby declare the following to be a full, clear, and exact descriptionof the invention, such as will enable others skilled in the art to'whichit appertains to make and use the same.

The present invention relates to an improved process for the production.by silicothermic reduction, of metals and alloys poor in carbon andsilicon. More especially it is intended for the production of metals andalloys practically free from carbon (i. c. with less than 0.25% C.) andpoor in silicon, such as, for example,'a ferro-chromium alloy or aterm-manganese alloy.

When a substance containing oxygen compounds, such for example, as anore containing metallic oxides, is reduced with silicon, for example inthe form of a highsilicon alloy with more than 10% of silicon, alow-carbon metal or low-carbon alloy as well as a silicate slag are,obtained, if the reduction is carried outunder such Well knownconditions that no carbon is supplied from outside during the process.If the metal or alloy reduced is moreover to be poor in silicon, theoxidizing agent must be supplied in excess, resulting in the formationof a slag as a by-product rich in metal oxides, the content of thelatter being high when the silicon content of the metal or alloyproduced is low, and vice versa.

If it is desired that the metal or alloy reduced by the silico-thermicprocess should be practically free from carbon, the reducing agentemployed must consist of silicon or a silicon alloy with a siliconcontent which should not be lower than but maybe higher, for example ormore.

The quantity of slag formed in the reduction, alloy wit at least 40% ofsilicon is employed, will be comparatively large, if the metal or alloyproduced is to be poor in silicon. ,The slag produced, as a generalrule, can beutilized only in part as raw -material in the manufacture ofa silicon articula'rly if pure silicon or an Appli'cationfiled December17, 1923. Serial No. 681,126.

alloy comparatively rich in silicon, for example a silicon alloy with upto about 40% Si. That this is'really the case is clearly illustrated bythe following reaction representing as nearly as possible actualconditions of practice. In this reaction Me designates a metal theatomic weight of which is lower than 56, for example Cr or Mn.

6Me,O,+3MeSi +8CaO= (metal oxide) (alloy with more than 40% Si)+(flux):9Me+2 (3MeOACaO3SiO,) (metal practically'free from carbon and'poor insilicon) +(silicate slag, rich in metal oxide).

The above reaction shows with sufficient clearness that the slagformedas a by-product contains twice as much metal as the quantity supplied tothe reduction process in the form of a silicide.

This defect in .the silico-thermic reduction process of yielding as abyroduct a quantity of slag rich in metals w ich cannot be completelyutilized with advantage is eliminated by our present process ofproducing low-carbon and low-silicon metals and alloys by thesilico-thermic reduction of ores. The characteristic and essentialfeature of the process is that the reducing agent consisting of siliconor silicon alloys relatively rich in silicon, preferably with at least40% of silicon, is first oxidized,

with an insufiicient quantity of oxidizing agent, such as an orecontaining metallic oxides, for forming an alloy poor in carbon andrelatively rich in silicon (but in all cases with a percentage ofsilicon, lower than that in the alloy which has been artially oxidized)and a silicate slag which is relatively poor in metal oxides. It will beunderstood that when the silicate slag is poor in metal oxides, thesilicon content of the metals or alloys formed generally will be high.The last-mentioned alloy relatively rich in silicon is then oxidizedwith an excess of ore, which results in the formation of a slag rich inmetal oxide, and a metal or alloy low in carbon and silicon. This slag,other circumstances being equal, is richer in metal oxide according asthe low-carbon metal or alloy is lower in silicon.

The essential advantage of our process, as compared with the olderrocess described above should be lufliclently clear from the followingrespresentative reac tlons, in which Me signifies the same as above:

Reaction Ia:

3Me O +Me ,Sad-411210:(metal oxide in insuilicient quantity) +(metalsilicide rich in silicon) (flux) :Mefih-l-MeOACaO. lSiO (metal silicidefor reaction Ib, sec below)+(silicate slag poor in metal oxide).Reaction Ib:

Me Si +3We O 4CaO (metal silicide from reaction Ia)+(metal oxide inexcess) flux l1 Me-l- 3 Me(). 4o 0. ElSiO UOW-carbon and low-siliconmetal) (silicate slag rich in metal oxide).

Reaction IIa:

3Me().4CaO.3SiO +MeSi,:(slag rich in metal oxide from reaction IIb ininsutfieient quantity (see below) (metal silicide rich in silicon).

3l\IeSi+l\Ie0. lCaO.4SiO (metal silicide for reaction IIb) (silicateslag poor in metal oxide).

Reaction IIb:

3Me O +3MeSi+4CaO -(metal oxide in excess) (metal silicide from reactionIIa) (flux) 6Me 3MeOxlCaO3SiO, (low-silicon metal practically free fromcarbon) (silicate slag rich in metal oxide used in reaction IIa).

Reaction IIa-l-IIb 3Me O -{MeSi 4CaO=6Me+MeO.4CaO. 4Si0 (metaloxide)+(metal silicide rich in silic n) (flux) (low-silicon metalpractica ly free from carbon) +(silicate slag poor in metal oxide).

It will be easily understood from the last group of formulae that ourprocess can be applied in such a way that no slag rich in metal oxideneed be obtained as a by-prodnot. It ought to be obvious that in theabove representative reactions pure metal oxide has been chosen asexample instead of ore. In principle there is no difference if the ore,in addition to one or more metal oxides reducible with silicon, shouldcontain also other substances. such as for example MgO, Al. SiO. and soforth.

in the reactions Ia, Ib, Ila and Ill), a silicon alloy of the same metalas that to be reduced from the ore'is given as an example of a reducingagent. Naturally there will be no essential change it a silicon alloy ofa metal other than that or those occurring in the ore is employed as'areducing agent. In the latter case the product will merely be an alloyinstead of an unalloyed metal. It should be evident from reaction IIathat it is possible to start from pure silicon instead of from a siliconalloy rich in silicon. Likewise it will be apparent from the samereaction that in the case of the silico-thermic production-of verycostly metals or alloys, it is possible to utilize completely even theslag: relatively poor in metal oxide as raw material for the productionof a reduction alloy.

Finally it should be mentioned in this connection that when in the abovewe speak '1 insufficient quantity or oi-e" in excess, we mean that thecontent of oxygen in oxides supplied to the process and reducible withsilicon is too small to be able to bind. or respectively too large to beentirely consumed in the binding of a quantity of silicon simultaneouslysupplied in the form of a silicon alloy.

The theoretic aspect of our process having thus been illustrated indetail by the above, we shall now, in order to elucidate it further,describe its practical application Seeing that, as we know, thesilico-thermic reduction in general proceeds endo-thermically, heat fromoutside must be supplied during thevarious stages of the process. Thepart or phase of the process in which an alloy relatively rich insilicon. for example with more than 40% of silicon, is partiallyoxidized (indicated by the reactions Ia and IIa), can be carried out ina Bessemer converter. In that case the necessary heat can be obtained bythe process that part of the silicon supplied is combusted with freeoxygen, e. g. in the. form of air. This process is rapid and yields aslag practically tree from metal oxide, but presupposes the conditionthat at least one of the necessary substances can be introduced into theconverter in a molten state. Obviously the same phase of the process canbe carried out in a suitable electric furnace, e. g. in a known manner.The part of the process which relates to the actual production of themetal or alloy poor in carbon and silicon is most advantageously carriedout, in a suitable electric furnace. Bessemerizing with air for thecarry-ingout of this latter stage entails difliculties in obtaining afinal product suiiiciently free from nitrogen.

By way of further elucidation, we shall finally, as an example, describethe production. in accordance with one mode of our process, of lowsilicon ferro-chromium practically free from carbon.

In a suitable electric furnace, e. a single-phase furnace in which thecurrent is supplied both through an adjustable carbon electrode andthrough the furnace lining, a slag bath rich in chromium is produced,for example by the smelting of a suitable quair tity of silicate slag.rich in chromium, from a previous process. The high chromium slag baththus produced is supplied with a suitably proportioned quantity offerrosilicochromium with more than 40%, e. g. 45%, of silicon. Thereaction between the substances supplied, provided that the proportionsbetween them. are properly proportioned. will yield firstly an alloypractically free from carbon with a lower silicon content than that inthe alloy originally supplied, and secondly a slag practically free fromchromium. The slag free from chromimn is tapped off and discarded whilstthe alloy free from carbon but relatively rich in silicon is transferredin a fluid or solid state to another similar electric furnace. in whichin the meantime a molten chromium ore bath has been arranged. Thereaction which takes place in this second furnace between the chromiumore bath and the silico-chromium alloy practically free from carbonsupplied to it from the first furnace will yield. if the quantities areproperly proportioned. a low-silicon ferrochromium practically free fromcarbon and a high-chromium silicate slag. which latter is transferred ina solid or fluid form to the first mentioned furnace in order to befreed there. in the manner indicated above. from the main part of itschromium content. whilst the carbon-free ferro-chromium from the secondfurnace is removed thence and allowed to solidify, or is used in amolten form for a suitable purpose, e. g. in order to form. togetherwith melted lowcarbon iron material for the production of stainlesssteel or iron. By choosing proportions between the silicon content inthe alloy supplied to the slag bath in the first furnace and in thealloy produced therein. it is possible to arrange that the high-chromiumslag obtained in the second furnace c'an entirely be consumed in thefirst furnace, for the manufacture of the quantity of silicochromiumalloy which is successively consumed in the other furnace.

It should be evident that the mode of our process which has beenexemplified above is also applicable to the. silicothermic production ofan alloy with a higher carbon content than 0.25%. in which case one canproceed from a ferro-silico-chromium alloy with less than 40% Si. It isalso manifest that it is not essential to our process that two furnaces,or two groups of furnaces, should be used. It. is possible also to useonly one furnace. in which case one may proceed. for example, as follows\Vhen the high-chromium. slag has been freed from the main part of itschromium content. it is removed in some suitable way. whereupon moltenchromium ore issupplied to the silico-chromium alloy retained in thefurnace. until that alloy has been sufficiently desilicized. whichresuts in the formation of a high-clnon'iium slag. which is retained inthe furnace whilst the alloy is being removed. whereupon a freshquantity of silico-chromimn alloy. is supplied by which the chromiumslag bath is partly de silicized. and so forth.

It is likewise evidentthat it-is possible in a single furnace to performone. stage or phase of the process for some length of time. in orderafterwards to use the furnace for some length of time for theperformance of the other part of the process.

Finally it should he mentionedthat our process is also direct applicablefor the manufacture of ferro-chromium poor in carbon and silicon andwith a relatively low content of chromium. e. g. 830% Cr, an alloy fromwhich stainless articles can be manu factured by a suitable process. Inorder to attain this object. it is obviously merely necessary to modifythe above described production of ferro-chromium (which as a rule meansan alloy with 60 to Cr) by supplying a suitable quantity of low-carboniron in a solid or molten form at a suitable moment during the first orsecond phase of the process.

It should also be evident from the above that fer'ro-manganese low incarbon and silicon can be produced from manganese ore in a manneranalogous to that described above.

Percentage in this specification and in the claims always means percentby weight.

Having thus described our invention we declare. that what we claim is 1.Process for the production of metals or alloys of low carbon and siliconcontent by silico-thermic reduction which comprises oxidizing an alloyhaving a relatively high silicon content with a metal oxide to produceasilicate slag relatively low in metallic oxides and a metallic silicidelow in carbon and relatively high in silicon. thereafter treating saidmetallic silicide with a metallic oxide to produce a metal relativelylow in carbon and silicon and a silicate slag relatively high inmetallic oxide. and separating the metal thus formed.

2. Process for the production of metals or alloys of low carbon andsilicon content by silico-thermic reduction which comprises oxidizing analloy having a relatively high silicon content with a molten silicateslag rich in metallic oxides to produce a silicate slagrelatively poorin metallic oxide and a metallic silicide low in carbon and relativelyhi h in silicon, thereafter treating said meta lic silicide with amolten metallic oxide to produce a low carbon and low silicon metal anda silicate slag relatively high in metallic oxide, and separating themetal thus formed.

3. Process for the production of metals or alloys of loW carbon andsilicon content by silico-thermic reduction which comprises supplying asolid alloy having a relatively hi h silicon content to a moltensilicate slag ric in metallic oxides to produce a silicate slagrelatively low in metallic oxides and a metallic silicide low in carbonand relatively high in silicon, thereafter supplying the metallicsilicide thus formed in solid form to a molten bath containing metallicoxides in an amount greater than the equivalent of the silicon contentof the metallic silicide to produce a metal relatively low in carbon andsilicon and a silicate slag relatively high in metallic oxides, andseparating the metal thus formed.

4. Process for the production of metals or alloys of low carbon andsilicon content by silico-thermic reduction which comprises 0x1- dizingan alloy having a relatively high silicon content with a metal oxide toproduce a silicate slag relatively low in metallic oxides and a metallicsiliclde low in carbon and relativel high in silicon, thereaftertreating sai metallic silicide with a metallic oxlde to produce an alloyrelatively low in carbon and silicon and a silicate slag relatively highin metallic oxide, and separating the alloy thus formed.

5. Process for the production of ferrochromium alloys having a lowcarbon and low silicon content by silico-thermic reduction whichcomprises oxidizing an alloy having a relatively high silicon contentwith a sillcate slag rich in chromium oxide to roduce a low carbonsilico-chromium a loy With a relatively high content of silicon and asilicate slag relatlvely poor in chromium oxide, supplying thesilico-chromium alloy thus formed in solid form to a molten bathcontaining ferro-chrome ore having a content of chromium oxide in amountexceedin the equivalent of the silicon content of sai silico-chromiumalloy to produce a ferrochromium alloy low in carbon and silicon and asilicate slag rich in chromium oxide, and separating 'the ferro-chromiumalloy thus formed.

In testimony whereof we have hereunto set our hands this 17th day ofNovember 1923.

SVEN DAGOBERT DANlELl. BO MICHAEL STURE KALLING.

In presence of OSCAR SKARBERG, OSCAR SWANBERG.

